Legal regulations concerning on-board diagnosis (OBD) in motor vehicles having an internal combustion engine require the recognition of emission-relevant errors in subsystems of the air charging system. Thus, legislation in California requires monitoring of the exhaust gas recirculation (EGR) in diesel engines and monitoring of the charge pressure regulation in gasoline and diesel engines having chargers, e.g. having exhaust gas turbochargers. European legislation requires the monitoring of the exhaust gas recirculation in diesel engines. In California legislation, inter alia the recognition of so-called slow response errors, relevant to emissions, is required. These are understood as a retarded response of the exhaust gas recirculation, or of the charge pressure, to a change in the target value, which can result in an increase in the exhaust gas emissions, up to values above OBD boundary values.
A retarded response of the exhaust gas recirculation can cause, for example in a diesel engine, an increase in emissions if a temporarily too-low EGR rate results in an increased combustion temperature and an increased oxygen excess, and thus an increase in nitrogen oxide emissions. In contrast, a temporarily too-high EGR rate can result in a reduced combustion temperature and a reduced oxygen excess, and thus an increase in soot emissions. A temporarily too-low or too-high charge pressure can cause disturbances in the air charging of the cylinders, so that the quantity or the time of the fuel injection or the EGR rate is no longer optimally adapted to the actual air charging, which can cause an increase in the exhaust gas emissions.
Various methods exist for the diagnosis of subsystems of the air charging system. For example, methods are known that monitor the intervention of the charging regulation when there is a change in the EGR target value. A stronger intervention of the charging regulation indicates a retarded response of the exhaust gas recirculation. Likewise, methods are known that model the charge pressure under the assumption of an error-free system and compare the model value to the measured charge pressure. If, when there is a change in the charge pressure target value, a large difference is recognized between the model value and the measured value, this is evidence of a retarded response of the charge pressure regulation.
Patent document DE 10 2011 088 296 A1 discusses a method and a device for carrying out the method for dynamic monitoring of gas sensors of an internal combustion engine, the gas sensors having a low-pass characteristic as a function of geometry, measurement design, aging, or contamination, and, given a change in the gas state quantity that is to be measured, a dynamic diagnosis being carried out on the basis of a comparison of a modeled signal and a measured signal, the measured signal being an actual value of an output signal of the gas sensor and the modeled signal being a model value. Here, it is provided that the output signal of the gas sensor is filtered using a high-pass filter, and, when there is a change in the gas state quantity that is to be measured, higher-frequency signal portions are evaluated. With this method, changes with regard to the dynamic behavior in gas sensors can be detected and quantified.
A related method, discussed in DE 10 2012 201 033 A1, can be used to ascertain a dead time of gas sensors.
The approaches discussed in DE 10 2011 088 296 A1 and DE 10 2012 201 033 A1 also offer approaches for providing a dynamic monitoring of an air charging system of an internal combustion engine with corresponding adaptation of the method.